1. Field of the Invention
The present invention relates to a trailing link type beam suspension and more particularly, to a beam suspension which is suitable for use as the rear suspension of a front-wheel drive automobile.
2. Description of the Prior Art
A trailing link type beam suspension has been proposed wherein one of a pair of left and right trailing arms is fixed to an axle beam whereas the other is rotatably connected to the axle beam in order that left and right wheels may be moved up and down freely. One example of such a trailing link type beam suspension will be described with reference to FIGS. 1 and 2. Left and right wheels 1 and 2 are rotatably supported on axles 3 and 4, respectively. Axle beam 5 secured and connected to the axles 3 and 4, respectively, are arranged below the axes Q of rotation of these wheels 1 and 2. A pair of left and right trailing arms 6 and 7 are respectively connected between the chassis (not shown) and axles 3 and 4 in order to permit vertical movement of the axle beam 5 with respect to the chassis and to resist lateral loads to control the back and forth movement. That is, in FIG. 1, the rear end of the left trailing arm 6 is fixed to the point of connection between the left axle 3 and axle beam 5, and the front end of the trailing arm 6 is connected to the chassis in such a way that it may be rotated around an axis O.sub.L. The rear end of the right trailing arm 7 is connected to the point of connection between the right axle 4 and axle beam 5 through a swinging bearing 8 in such a way that it may be rotated around the axis Q, and the front end of the trailing arm 7 is connected to the chassis in such a way that it may be rotated around an axis O.sub.R. Accordingly, when the left and right wheels 1 and 2 are moved up and down, the axle beam 5 swings up and down around the axes O.sub.L and O.sub.R. A pair of left and right coil springs 9 and 10 are provided between the axle beam 5 and the chassis in order to resiliently oppose the chassis, and a pair of left and right dampers 11 and 12 are provided in order to absorb vibration energies of the coil springs 9 and 10. The dampers 11 and 12 are obliquely and forwardly arranged between front ends 15, 16 of forwardly projected arms 13, 14 provided integrally with the axle beam 5 and the chassis. A panhard rod 17 is connected between the axle beam 5 and the chassis in such a way that it may be rotated around respective axes almost parallel with the longitudinal direction of the chassis, in order to control the lateral movement of the axle beam 5 with respect to the chassis.
In such a trailing link type beam suspension, for example, in the event that in FIG. 1, only the left-hand wheel travels over a projected portion of the road surface and moves up, the left end of the axle beam 5 is rotated around the axis O.sub.L by the trailing arm 6 and moves up. Since the axle beam 5 and trailing arm 6 are to each other, the axle beam 5 rotates clockwise as viewed from the right wheel in of FIG. 1. On the other hand, since the right-hand trailing arm 7 is rotatably connected to the axle beam 5, the tailing arm 7 is not affected by the rotation of the axle beam 5. That is, the right-hand trailing arm 7 is never swung to follow the vertical movement of the left-hand wheel 1, and thus, the right-hand wheel 2 is maintained in its unchanged state.
Incidentally, since the axle beam 5 is rarely subjected to torsional deformation, rotation of the left end of the axle 5 at that time is transmitted to the right end without modification. Accordingly, at this time, the arm 14 integrally provided on the right end of the axle beam 5 is rotated clockwise as viewed from the right wheel in FIG. 1, that is, counterclockwise in FIG. 2, and the front end 16 thereof moves down. The center of rotation is substantially the axis Q, and therefore, the damper 12 is drawn considerably downwardly. Therefore, an attentuation force is generated in the damper 12, as a consequence of which there occurs a problem that the chassis rocks to deteriorate riding comfort.
Since a tension is applied to the damper 12 as described above, if the coil spring 10 is provided for the damper 12, the riding comfort further deteriorates. Therefore, mounting portions for the coil spring 10 have to be provided, separately from the mounting portion for the damper 12, on the axle beam 5 and chassis. And, the coil spring 9 needs be mounted in symmetry with the coil spring 10, and therefore, the mounting portion for the coil spring 9 has to be also provided separately from the mounting portion of the damper 11.
In addition, the trailing link type suspension of the type as described is not possible to make the rigidity of the trailing arms 6 and 7 great with respect to the lateral load of the chassis. In view of this, the panhard rod 17 is provided between the axle beam 5 and chassis to resist said load. This panhard rod 17 is arranged adjacent to the axle beam 5. However, the coil springs 9, 10 are provided on the axle beam 5 as previously described, and therefore, normally, a rearwardly projected arm 18 is provided on one end of the axle beam 5, and one end of the panhard rod 17 is connected to the foremost end of the arm 18 in such a way that it may be rotated around an axis substantially parallel to the longitudinal axis of the chassis whereas the other end of the panhard rod 17 is likewise rotatably connected to the chassis by means of the point of connection 19 to the chassis. This panhard rod 17 is arranged such that the point of connection 19 to the chassis is spaced further from the axle beam than the point of connection to the axle beam 5 to prevent interference with the axle beam 5 when the latter is moved up and down by the trailing arms 6 and 7. Thus, the point of connection 19 to the chassis of the panhard rod 17 is considerably spaced rearwardly from the axis of rotation Q of the wheels 1 and 2 in plan view, as can be seen in FIG. 1.
In the arrangement as described above, when lateral forces are applied to the wheels 1 and 2 during turning of the vehicle, this results in a moment of rotation of the suspension system around the point of connection 19 of the panhard rod 17 to the chassis. Generally, rubber bushings are inserted at the points of connection between the trailing arms 6, 7 and the chassis, and therefore, the bushings are sometimes deformed by the moment of rotation which impairs the steering stability of the vehicle. If the spring constant of the rubber bushings is suitable to maintain the steering stability, vibrations from the axle beam 5 are transmitted to the chassis to deteriorate the riding comfort.